Microstrip line filter combining a low pass filter with a half wave bandpass filter

Abstract

A plurality of composite elements are arranged in parallel with each other on a substrate. The composite elements each include a rectangular microstrip line element, an input microstrip line and an output microstrip line. The microstrip line element has one longer side, the other longer side, one end and the other end, and the input microstrip line is connected at the one end to the one longer side while the output microstrip line is connected at the other end to the other longer side. The composite elements are cascaded to constitute a low-pass filter.

What is claimed is:  
     
       1. A microstrip line filter formed on a substrate, comprising a plurality of composite elements arranged in parallel with each other, said composite elements each including a rectangular microstrip line element, an input microstrip line and an output microstrip line that are formed on said substrate, and said composite elements being connected to constitute a low-pass filter, wherein 
       said composite elements adjacent to each other have respective input microstrip line and output microstrip line connected to each other.  
     
     
       2. The microstrip line filter according to  claim 1 , wherein 
       rectangular microstrip line elements of said composite elements differ in the length of longer side.  
     
     
       3. The microstrip line filter according to  claim 2 , wherein 
       said rectangular microstrip line elements include outer microstrip line elements and inner microstrip line elements and  
       said inner microstrip line elements have longer sides shorter than those of said outer microstrip line elements to obtain desired input/output impedance characteristics, in-band pass characteristics and out-of-band attenuation characteristics.  
     
     
       4. The micro strip line filter according to  claim 1 , wherein 
       a half-wave bandpass filter connected in series to said low-pass filter is further formed on said substrate.  
     
     
       5. The microstrip line filter according to  claim 4 , wherein 
       said half-wave bandpass filter includes a plurality of rectangular microstrip line elements arranged in parallel with each other at predetermined intervals and inclined at a certain angle, and halves of respective longitudinal sides of said microstrip line elements are opposite to halves of respective longitudinal sides of adjacent microstrip line elements.  
     
     
       6. The microstrip line filter according to  claim 1 , wherein 
       said rectangular microstrip line element has one longer side, the other longer side, one end and the other end,  
       said input microstrip line is connected at said one end to said one longer side, and  
       said output microstrip line is connected at said other end to said other longer side.  
     
     
       7. The microstrip line filter according to  claim 1 , wherein 
       the adjacent composite elements are symmetrical with respect to a center line between the input microstrip line and the output microstrip line connected to each other.  
     
     
       8. The microstrip line filter according to  claim 1 , wherein 
       microstrip line elements of said composite elements are arranged symmetrically with respect to a center line of the arrangement of said composite elements, and  
       said microstrip line filter includes a metal casing having a partition on said center line and covering microstrip line elements of said composite elements.  
     
     
       9. The microstrip line filter according to  claim 1 , wherein 
       microstrip line elements of said composite elements have respective input microstrip lines and respective output microstrip lines that connect the microstrip line elements and that have respective widths selected to obtain desired input/output impedance characteristics, in-band pass characteristics and out-of-band attenuation characteristics.  
     
     
       10. A high-frequency transmitter converting an intermediate-frequency signal into a high-frequency signal and transmitting the high-frequency signal, comprising: 
       a mixer circuit combining said intermediate-frequency signal with a local oscillator signal;  
       a filter circuit connected to an output of said mixer circuit; and  
       a high-frequency amplifier circuit connected to an output of said filter circuit,  
       said filter circuit being formed on a substrate and including  
       a half-wave bandpass filter including a plurality of rectangular microstrip line elements arranged in parallel with each other at predetermined intervals and inclined at a certain angle, halves of respective longitudinal sides of said microstrip line elements being opposite to halves of respective longitudinal sides of adjacent microstrip line elements and  
       a low-pass filter including a plurality of composite elements arranged in parallel with each other and cascaded, said composite elements including respective rectangular microstrip line elements, respective input microstrip lines and respective output microstrip lines,  
       wherein 
       said composite elements adjacent to each other have respective input microstrip line and output microstrip line connected to each other.  
     
     
       11. A microstrip line filter formed on a substrate, comprising a plurality of composite elements arranged in parallel with each other, said composite elements each including a rectangular microstrip line element, an input microstrip line and an output microstrip line that are formed on said substrate, and said composite elements being cascade connected to each other on the substrate to constitute a low-pass filter.